1. Field of the Invention
This invention relates to a method of preparing a boratabenzene-containing metal complex.
2. Background Art
The usefulness of olefin polymerization catalysts containing a transition metal pi-bonded to a ligand that contains a boratabenzene ring has recently been realized. Such catalysts may be used in the homo- and co-polymerization of ethylene and other olefinic hydrocarbons. These catalysts offer several advantages over the conventional Ziegler catalyst systems which contain a transition metal and one or more organometallic compounds. Specifically, the boratabenzene-containing catalysts have exhibited higher activities, thereby making it feasible to use a lesser amount of the catalyst. Lower concentrations of the boratabenzene catalysts have made it less important to remove catalyst residues. Conventional catalysts have required that neutralizing agents and stabilizers be added to the polymers to overcome the deleterious effects of the catalyst residues. Failure to remove residues results in polymers having a yellow or grey color and poor ultraviolet and long term stability. Chloride-containing Ziegler catalysts can cause corrosion in polymer processing equipment. Ziegler catalysts tend to produce polymers with a broad molecular weight distribution, which is less desirable for injection molding applications. Furthermore, Ziegler catalysts are not very efficient at incorporating xcex1-olefin co-monomers, thereby making it difficult to control polymer density.
Although Ziegler catalysts have been improved, these catalysts are being replaced with metallocene catalyst systems. A metallocene consists of a transition metal with two or more cyclopentadienyl ligands attached. The metallocene catalysts have low activities when used with organometallic co-catalysts such as aluminum alkyls, but have high activities when used with aluminoxanes as co-catalysts. Activities are so high that it is not necessary to remove the catalyst residue from the polymer. These catalysts also incorporate xcex1-olefins well. However, at high temperature they tend to produce lower molecular weight polymers. As such, they are most useful for gas phase and slurry polymerizations of ethylene which are typically conducted between 80 and 95xc2x0 C. The improved co-polymerization of ethylene is desirable because it allows greater flexibility for producing polymers over a wider range of densities as well.
Relatively few synthetic routes to boratabenzene-containing compounds are known. An early route was the hydrostannylation of 1,4-pentadiyne with dibutylstannane to give boracyclohexadiene on exchange with boron halides. Boracyclohexadiene is then deprotonated with a base such as lithium diisopropylamide (LDA) to give lithium boratabenzene. However, 1,4-pentadiyne tends to be unstable and somewhat difficult to prepare in high yields. Another route for preparing boratabenzene is based on the metalation induced ring closure of [bis(dialkylamino)boryl]pentadienes. Improved methods of preparing boratabenzene-containing compounds in high yield and high volume are needed.
The present invention provides a method for preparing a boratabenzene derivative or a boratabenzene-containing complex. Boratabenzene has the following formula: 
where R is hydrogen, a C1-8 alkyl group, C6-10 aryl group, C7-15 aralkyl group, C1-10 alkoxy group, C6-14 aryloxy group, C1-8 dialkylamino group, or C6-15 diarylamino group.
In one embodiment of the present invention an improved method for forming a 1,4-pentadiyne is provided. The 1,4-pentadiyne is formed by reacting an alkynyl magnesium bromide with an alkynyl benzenesulfonate in a first solvent. A second solvent is added to the reaction vessel to form a second solution. The second solution is distilled and a third solution comprising the second solvent and the 1,4-pentadiyne is collected. This second solvent is suitable for the next step in the preparation of the boratabenzene derivative. In this preparation, the 1,4-pentadiyne is not directly separated from at least one solvent. This is advantageous because 1,4-pentadiyne compounds are unstable and reactive. The 1,4-pentadiyne is reacted with a dialkytin dihydride to form a 1,1-dialkylstannacyclohexa-2,5-diene.
In another embodiment of the present invention, the 1,1-dialkylstannacyclohexa-2,5-diene is reacted with a boron trihalide and then an alkylating agent to form a 1-alkylboracyclohexa-2,5-diene. The 1-alkylboracyclohexa-2,5-diene is converted into a boratabenzene by reaction with a strong base. In another embodiment of the present invention, the 1,1-dialkylstannacyclohexa-2,5-diene is reacted with a alkylboron dihalide or an arylboron dihalide to form the corresponding 1-alkyl- or 1-arylboracyclohexa-2,5-diene. The 1-alkylboracyclohexa-2,5-diene is reacted with a strong base to form a 1-alkylboratabenzene derivative.
In still another embodiment of the invention, a 1,1-diakylstannacyclohexa-2,5-diene suitable for preparing a boratabenzene-containing complex is provided. This embodiment is suitable for any preparation of a boratabenzene derivative that utilizes a 1,1-diakylstannacyclohexa-2,5-diene derivative. Polymethyihydrosiloxane, potassium fluoride, a catalytic amount of 2,2-azobisisobutyronitrile, a 1,4-pentadiyne derivative, and a dialkytin dihalide are reacted together. This reaction produces a 1,1-dialkylstannacyclohexa-2,5-diene in high yields. A 1-alkylboratabenzene and a boratabenzene-containing complex are formed as described above.
In yet another embodiment of the present invention, an improved method for preparing a 1-chloroboracyclohexa-2,5-diene is provided. In this embodiment, 1,1-dibutylstannacyclohexa-2,5-diene is reacted with a boron trihalide in a first solvent to form the 1-chloroboracyclohexa-2,5-diene. A second less volatile solution is then added and the first solvent is removed under vacuum. This second solvent is suitable for the next step in the preparation of the boratabenzene derivative as described above.
Reference will now be made in detail to presently preferred embodiments and methods of the invention, which constitute the best modes of practicing the invention known to the inventors.
In accordance with one embodiment of the invention, a presently preferred method of preparing a boratabenzene complex is provided. The method of the present invention comprises the preparation of a 1,4-pentadiyne derivative. The 1,4-pentadiyne derivative is prepared by forming a first reaction solution comprising an alkynyl magnesium bromide with an alkyipropargyl benzenesulfonate and a catalytic amount of copper (I) bromide in an inert solvent. The preferred alkynyl magnesium bromide has the formula: 
where R1 is hydrogen, a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group. The preferred alkynyl magnesium bromide is ethynyl magnesium bromide. The alkylpropargyl benzenesulfonate has the formula: 
where R2 is hydrogen, a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group. The alkynyl magnesium bromide is preferably made by anion exchange by reacting an alkynyl magnesium chloride with a bromide salt such as lithium bromide. The preferred inert solvent for performing the reaction will typically be an ether. The preferred solvent is di(ethylene glycol) dibutyl ether. After the reaction is complete, a second solvent is added to form a second reaction solution. The second solvent must be chemically unreactive with regards to the 1,4-pentadiyne derivative which is formed during the reaction. Furthermore, this second solvent is more volatile than the first solvent. Preferred second solvents are toluene and benzene. This second solution is then distilled and a third solution comprising the 1,4-pentadiyne derivative and the second solvent is collected. This second solvent is suitable for the next step in the preparation of the boratabenzene derivative. The structure of the 1,4-pentadiyne derivative is: 
The third solution is reacted with a dialkyl tin dihydride having the formula: 
where R3 is a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group or a C1-10 alkyl group and R4 is a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group. The resulting product of this reaction is a 1,1-dialkylstannacyclohexa-2,5-diene having the formula: 
This 1,1-dialkylstannacyclohexa-2,5-diene is then reacted with a boron halide with the formula:
BX3xe2x80x83xe2x80x83(VII)
where X is a halogen to form a 1-haloboracyclohexa-2,5-diene having the formula: 
In a particularly preferred embodiment, the preferred boron halide is boron trichioride.
The 1-haloboracyclohexa-2,5-diene derivative is next reacted with an alkylating agent to form a 1-alkylboracyclohexa-2,5-diene derivative having the formula: 
where R5 is a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group. The preferred alkylating agents are trialkylaluminum and dialkylzinc compounds. The preferred alkylating agents are trimethylaluminum, triethylaluminum, dimethylzinc, and diethylzinc.
The 1-alkylboracyclohexa-2,5-diene derivative is next reacted with a strong base to form a 1-alkylboratabenzene having the formula: 
Finally, the 1-alkylboratabenzene is converted to a boratabenzene-containing metal complex by reacting the 1-alkylboratabenzene with a transition or lanthanide metal complex. Preferred transition or lanthanide metal complexes include CpZrCl3 (Cp=cyclopentadienyl group).
In another embodiment of the present invention, the boron halide that is reacted with the 1,1-dialkylstannacyclohexa-2,5-diene derivative described by structure VI has the formula:
R5BX2xe2x80x83xe2x80x83(XI)
where R5 is a C1-10 alkyl group, a C6-10 aryl group, or a C7-15 aralkyl group and X is a halogen. The resulting product of this reaction is 1-alkyl boracyclohexa-2,5-diene given by formula IX. The 1-alkylboracyclohexa-2,5-diene derivative is next reacted with a strong base to form the 1-alkylboratabenzene given by formula X.
Finally, the 1-alkylboratabenzene is converted to a boratabenzene-containing complex by reacting the 1-alkylboratabenzene having with a transition or lanthanide metal complex. Preferred transition or lanthanide metal complexes include CpZrCl3 (Cp=cyclopentadienyl group).
In another embodiment of the invention, a 1,1-diakylstannacyclohexa-2,5-diene suitable for preparing a boratabenzene-containing complex is provided. The 1,1-diakylstannacyclohexa-2,5-diene is used to prepare the boratabenzene-containing complex as described above. Alternatively, this embodiment is suitable for any preparation of a boratabenzene-containing complex that utilizes a 1,1-diakylstannacyclohexa-2,5-diene derivative. In this embodiment, polymethyihydrosiloxane, potassium fluoride, a catalytic amount of 2,2-azobisisobutyronitrile, the 1,4-pentadiyne derivative with structure IV, and a dialkytin dichloride are reacted together. The dialkyltin dichloride has the following structure: 
This reaction produces the 1,1-dialkylstannacyclohexa-2,5-diene described by structure VI in high yields. A 1-alkylboratabenzene and a boratabenzene-containing complex are formed as described above.
In another embodiment of the invention, an improved method for preparing a 1-haloboracyclohexadiene such as 1-chioroboracyclohexadiene suitable for preparing a boratabenzene-containing complex is provided. In this embodiment, 1,1-dibutylstannacyclohexa-2,5-diene is reacted with a boron trihalide such as boron trichioride in a first solvent. Upon completion of the reaction a second solvent is added to the reaction mixture. Both the first solvent and the second solvent must be chemically unreactive towards the reactants and products formed from this reaction. Furthermore, the first solvent has a greater volatility than the second solvent and the second solvent must be a suitable solvent for the next step in the preparation of the boratabenzene derivative. Preferred first solvents include methylene chloride and chloroform, and preferred second solvents include low chain hydrocarbons such as heptane, octane, nonane, decane, and mixtures thereof. Next, the first more volatile solvent is removed at a reduced pressure to form a solution comprising the reaction product, a 1-haloboracyclohexadiene such as 1-chloroboracyclohexadiene and the second solvent. In the next step, this solution is distilled yielding a second solution comprising 1-chloroboracyclohexadiene and the solvent. This second solution may be used directly without further isolation of the 1-haloboracyclohexadiene to produce the 1-alkylboratabenzene derivative and a boratabenzene-containing complex as described above. This embodiment is particularly useful in preparing 1-chloroboracyclohexadiene which is relatively unstable and difficult to isolate, being at the same time a key intermediate in boratabenzene derivatives synthesis.